FIGS. 3A to 3C show an example of a schematic configuration of a hard disk drive (Hereinafter, also referred to as HDD). This HDD includes a magnetic disk (a hard disk) 2 which records information (data), a spindle motor 4 which rotates the magnetic disk 2, a swing arm 8 as an actuator at a distal end portion of which a magnetic head 6 is mounted, and a voice coil 9 which is provided at a proximal end portion of the swing arm 8 to drive to rotate the swing arm 8.
The swing arm 8 is pivoted rotatably on a base Bs of the HDD via a pivot bearing unit 10 and moves the magnetic head 6 in parallel to (or causes the magnetic head 6 to trace) the rotating magnetic disk 2 when driven to rotate by the voice coil 9. By doing so, In the HDD, information can be read from the magnetic disk 2 or can be written (recorded) onto the magnetic disk 2 via the magnetic head 6.
Provided on the pivot bearing unit 10 are a shaft 12 which is erected on the base Bs of the HDD, a sleeve 18 on which the swing arm 8 is mounted, and pivot bearings 14, 16 which are interposed between the shaft 12 and the sleeve 18.
Additionally, the pivot bearings 14, 16 include inner rings 14a, 16a and outer rings 14b, 16b as pairs of bearing rings, pluralities of balls 14c, 16c as rolling elements which are assembled between the pairs of bearing rings so as to roll therebetween, and cages 14d, 16d which hold individually the balls 14c, 16c. In addition, non-contact type seal members 14e, 16e are interposed between the bearing rings so as to seal up interiors of the bearings individually, whereby not only is the intrusion of foreign matters (for example, dust particles) from the outside of the bearings into the interiors thereof prevented, but also the leakage of a grease composition placed in the interiors of the sealed bearings to the outside thereof is prevented.
Then, the pivot bearings 14, 16 support the swing arm 8 which is mounted on the sleeve 18 rotatably in such a state that the inner rings 14a, 16a are fitted on the shaft 12 and the outer rings 14b, 16b are fitted in the sleeve 18. Additionally, an annular spacer 20 is fitted in an inner circumferential portion of the sleeve 18 so as to be interposed between the pivot bearings 14, 16. By dosing so, the pivot bearings 14, 16 are positioned fixedly in a predetermined position while being preloaded in a predetermined fashion, whereby the pivot bearings 14, 16 can be rotated stably without rattling, which enables the swing arm 8 to rotate smoothly with good response.
In recent years, with a tendency to require higher density and higher capacity on hard disks (HDDs) increasing, higher mechanical accuracy and higher cleanness are also required in the interior of such hard disks. When foreign matters stick to a magnetic disk or a read head in the interior of an HDD, the performance thereof is deteriorated or a program error is triggered, and in the worst case, a failure of the HDD is called for. Therefore, higher cleanness is required in the interior of the HDD.
As one form of foreign matters generated in the interior of the HDD, there are outparticles which result from grease in a pivot bearing unit which supports an actuator. The grease in the interior of the pivot bearing unit is stirred as bearings work, whereby oil contents in the grease are discharged as a minute amount of particles, which stay in suspension in the interior of the HDD, eventually sticking to the magnetic disk and/or the read head.
Raised as methods for reducing outparticles are, for example, a method for narrowing a shield labyrinth of a bearing and a method as described in Patent Literature 1 for capturing particles by making use of the force of static electricity by forming a bearing seal member of a material having electrifying properties.
Additionally, in a hard disk drive pivot assembly described in Patent Literature 2, as shown in FIG. 6, a hub cap 140 is disclosed which is fixed to a shaft 110 so as to prevent gas or dust particles produced from grease provided in ball bearings 120 from being discharged to the outside of the assembly. This hub cap 140 is made up of an inner circumferential portion 141 and an outer circumferential portion 142 which is formed thinner than the inner circumferential portion 141.